New parts or used parts. New parts are hard to find but can be had at some Apple Authorized Service Providers and sometimes other places like iFixit. Used parts are like used cars, some have a lot more milage than others. iFixit prices are higher (sorry boys, but you know they are), but I only have to order the part once because its been tested and cleaned. When there are variations in wear, iFixit states so and gives different prices. For me buying on eBay or Craigslist is a crap shoot. Or as Forest Gump says , "a box of chocolates". I do buy a machine on eBay about once a month, but I look for the ones that state what is wrong or ones that they don't know what is wrong. My thought is that if a Mac is working OK, most people don't want to sell it unless that's their business.